The present invention relates, in general to the field of conditioning dry, compacted masses of tobacco and, more particularly, to an apparatus and a method for restoring moisture and flexibility to tobacco.
As is well known in the art, raw tobacco is often stored and shipped in dry, compacted masses, either as bales, which are generally rectangular cross-section, or in hogsheads, which are of generally circular cross-section. Although compacting of the tobacco provides convenient and efficient storage and shipping, it makes the tobacco difficult to handle in the manufacturing process, for the tobacco leaves become brittle and readily degrade into fine particles when the bales or hogsheads are opened. For manufacturing purposes, it is necessary to separate the leaves, and to do this, it is necessary to restore moisture and flexibility to the compacted tobacco masses. Such conditioning of the tobacco is accomplished in the prior art by exposure of the tobacco to a conditioning agent, which is normally steam.
A variety of systems have been devised for conditioning tobacco, and in general five parameters determine the usefulness and desirability of such a system. First, a viable system must provide a high volume operation in order to keep pace with other production equipment. Second, the system should be as economical as possible in terms of the cost of both equipment acquisition and operation. Third, the system should consume as little steam as possible, in order to minimize the energy expenditure required to condition a given volume of tobacco. Fourth, a viable system should produce as little particulate tobacco dust (fines) as possible so as to maintain a healthy working environment. Finally, the tobacco must be conditioned uniformly to prevent the formation of pads and clumps of leaves, to eliminate the need for reprocessing, and to eliminate poor quality, wasteage or increased particulate production.
The traditionally used conditioning system is a simple rigid vacuum chamber into which the tobacco to be treated is placed, the chamber then being evacuated and steam introduced. Such devices, which are exemplified by the Thermo-Vactor chamber or by the VacuDyne system can typically process about 12,000 lbs. of tobacco in about 35 minutes depending on the number of hogsheads for which a particular system is designed, but these devices are costly both in terms of capital investment and steam consumption. Additionally, a considerable direct labor cost is incurred in loading batches of tobacco on pallets and in filling and emptying the chamber, these being the inherent drawbacks of a batch processing system.
Another method that has been used in the prior art is to break the masses of tobacco into smaller pieces and feed them into a revolving steam drum. The combination of agitation and steam conditions the tobacco, but also produces a high level of particulate scrap or fines, i.e. particles of tobacco sufficiently small to pass through a 3/8 inch mesh screen. In addition, the direct labor cost is high, as is steam consumption.
An alternative technique is taught by Philbrick in U.S. Pat. No. 3,124,142, wherein a mass of tobacco is placed within a chamber and a perforated probe is inserted therein. Steam is then introduced into the chamber and a vacuum is connected to the probe so that the steam is gradually drawn through the mass of tobacco and evacuated through the probe, conditioning the tobacco as it passes. This type of equipment is more costly than the simple steam chamber process, however, and uses practically as much steam, even though it does improve the uniformity of conditioning over the steam chamber. In addition to retaining the inherent inefficiencies of batch processing, however, this procedure is not adapted to the processing of small bales of tobacco, and thus is not useful in many applications.
A variation of the probe technique taught in the foregoing patent is shown in U.S. Pat. No. 3,838,698 to Dickenson. In this patent, a tobacco mass is fed into a rectangular chamber, where belt conveyors force it against a probe. Steam is introduced into the space between the back of the chamber and the front of the mass, and a vacuum is applied to the probe, so that the steam is drawn through the front space of the tobacco mass. "Doffers" at the back of the chamber strip off successive layers of tobacco as the mass advances, and the stripped tobacco falls out of an aperture in the chamber floor. The most serious problem with this device is that its output is severely limited for the tobacco mass is said to advance at a rate of 90 mm per minute. Thus, a 30 inch bale would require almost 8 minutes conditioning time, and 45 of the Dickenson devices would be required to match the output of a single Thermo-Vactor chamber. Although speeding up the process would improve productivity, it would also lead to serious particulate problems from the increased stripping action of the doffers.
Attempts have been made to overcome the problems encountered in the steam chamber methods discussed above, including the use of multiple probes for injecting steam into a bale of tobacco. In such devices, the probes are mounted on a horizontal manifold which is lowered onto a bale of tobacco to insert the probe into the bale. Steam is then supplied under pressure into the tobacco bale. The steam continues to flow until the bale is heated and moisturized to the desired degree, and thereafter the probes are removed.
Although such systems are an improvement over prior devices, both from the standpoint of effective conditioning of the tobacco and from the standpoint of cost, a number of problems still remain which have prevented widespread use of the devices. Thus, for example, it was found that when multiple probes are used, it requires a great deal of force to insert all of the probes into the tobacco bale, which is tightly compacted. Further, it was found that in order to avoid unacceptable damage to the tobacco, it was necessary to make the probes of relatively small diameter. But this small diameter, combined with the forces required to insert the probes, often result in the probes bending during attempts to insert them, thus making them unuseable. Further, it was found that the steam would only travel short distances from the probes, and under high pressure would tend to seek the interface between layers of tobacco to escape from the bale, thus producing a nonuniform conditioning of the tobacco. In addition, because of the compactness of the bales once the probes were inserted it was difficult to remove them, for the bales tended to stick to the probes. Thus, rapid operation of these conditioning devices was virtually precluded, and accordingly multiple probe devices have not found acceptance in the industry.
Thus, there exists a need for an improved system for conditioning tobacco at a reduced cost, while retaining the quality of the product at an acceptable level, maintaining or increasing the rate of operation, and keeping a low level of particulates.